The present disclosure relates generally to laser welding, and more particularly to an apparatus for laser welding.
Laser welding is a fusion welding process, where materials are joined by melting or softening the interface between the parts to be joined and allowing it to solidify. An intense beam of laser radiation is focused onto the material to be joined. The radiation excites a resonant frequency in the molecules of the parts to be joined, resulting in heating of the material. The radiation produced by laser diodes may be used to weld plastic parts, but the power associated with a single laser diode may, in some instances, be insufficient to melt the material to be joined quickly and efficiently. Some laser welding devices combine the output of a number of laser diodes to produce quick heating of a large area of the material to be joined. One method for combining the laser radiation from a bank of laser diodes is to use optical fibers to transmit the laser radiation to a location to produce sufficient radiation density for welding. The flexibility of optical fibers may be advantageous in applications where welding is desired in three spatial dimensions.
The bank of lasers of one laser welding system contains 15 individual 50 Watt laser diodes for a combined power of 750 Watts. The laser diodes specified in the bank of lasers each produce continuous laser radiation at a wavelength of 808 nm with a spectral width less than 2.5 nm. The relatively tight spectral width may be advantageous when using the lasers as a bumping source for solid state lasers, however a tight spectral width generally corresponds to low energy gain efficiency in laser diodes.
Depending upon the application, there may be a relatively high cost of maintenance for both diode lasers and the optical fiber array. In a mass production environment, there may be a significant cost of down time if any of the 15 laser diodes or optical fibers requires realignment or maintenance. The mean time between maintenance (MTBM) of the system is generally shorter because of the relatively large number of components. Another drawback to an optical fiber array is the potentially high loss of energy during beam transportation through the fiber(s).
A laser welding apparatus may produce a line of sufficient laser energy density for welding by arranging segments of laser energy in an adjacent, linear array to create a substantially continuous line of laser energy with a length approximating the sum of the lengths of the individual laser segments. Welding may be relatively quickly accomplished by scanning the pieces to be welded substantially perpendicularly to the laser line. Consistent weld quality along the laser line may be accomplished by adjusting the power to each individual laser so that the laser energy absorbed by the welded parts is substantially equal for each laser line segment. However, individual control of the power to each laser diode may potentially be relatively expensive. As such, some laser welders may provide a single power control for the array of laser diodes; and in this case, if one laser drops in efficiency, it may, in some instances, not be possible to compensate by increasing the power to the array without potentially exceeding the specifications for the other laser diodes in the array. One strategy for overcoming a loss of efficiency in a laser diode may be to temporarily take the laser welder out of service and replace the less efficient laser diode.
Thus, it would be desirable to provide an apparatus for laser welding that substantially overcomes the above drawbacks by providing an apparatus that has a longer mean time between maintenance (MTBM), lower initial capital cost and more energy efficient operation.